The present invention relates to an electronic device for detecting the weight or passage of objects, to methods for installing such devices, and to applications of such devices to detection of the passage of or the presence of vehicle wheels.
A number of systems are already known for detecting vehicle axles or wheels. For example, it is known to carry out measurements for detecting axles using pneumatic tubes. Pressure variation inside the tubes is measured during the passage of an axle. Such systems are sensitive to pressure variation, but they cannot easily detect the presence of an axle.
Also known are devices which include two deformable metal blades adhesively bonded to, or held by any other means against, two opposed faces of a rubber component. The metal blades are separated by an air gap, and form a mechanical switch. When an object bears on the rubber component, the rubber component deforms, making a metal/metal contact which serves as the switch.
This system has a number of drawbacks, such as the difficulty of adhesively bonding mechanical components to rubber, which can considerably reduce the lifetime of the system. Moreover, such systems are extremely rigid along their length, making them barely deformable. As a result, it becomes very difficult to install or replace the sensors in a metal support component without an adhesive bonding or a mechanical mounting.
Systems are also known for measuring variations in resistance in layers of carbon-filled foam. These components have the drawback of having long response times, which can vary over time due to their aging.
Systems are also known (for example, from French Patent No. 2 634 926) which make use of a detection device having, on one side of the device, two elongate, fixed conductors placed opposite an elongate component made of a deformable conductive rubber.
The system of the present invention improves upon the system described in French Patent No. 2 634 926. To this end, a pressure-sensitive electrical switch is provided which uses the properties of a carbon-filled rubber, or other conductive element, for making the component electrically slightly resistive. The resulting sensors use a measurement of the electrical resistance between a partially insulated steel blade and a slightly resistive rubber component during the passage of vehicles.
The present invention also relates to techniques for installing the sensor (i.e., the device intended to receive the sensor), which can be anchored into the roadway by any known means, and to fitting and dismantling techniques which are made possible by the flexibility of the detection sensor.
Further characteristics and advantages will appear in the course of the description which follows.